fix: be lenient about KeyPackage lifetime when joining via external c…

…ommit

openmls/src/group/core_group/new_from_external_init.rs

@@ -52,7 +52,7 @@ impl CoreGroup {
             verifiable_group_info,
             // Existing proposals are discarded when joining by external commit.
             ProposalStore::new(),
-            true,
+            false,
         )
         .await?;
         let group_context = public_group.group_context();